Weathering is the decomposition of rocks, soils and their minerals through direct contact with the Earth's atmosphere. Weathering occurs in situ, or "with no movement", and thus should not to be confused with erosion, which involves the movement and disintegration of rocks and minerals by agents such as water, ice, wind and gravity. Rock redirects here. ... Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland For the American hard rock band, see SOiL. For the System of a Down song, see Soil (song). ... For other uses, see Mineral (disambiguation). ... Air redirects here. ... For morphological image processing operations, see Erosion (morphology). ...

Two important classifications of weathering processes exist. Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions such as heat, water, ice and pressure. The second classification, chemical weathering, involves the direct effect of atmospheric chemicals, or biologically produced chemicals (also known as biological weathering), in the breakdown of rocks, soils and minerals.

The materials left over after the rock breaks down combined with organic material creates soil. The mineral content of the soil is determined by the parent material, thus a soil derived from a single rock type can often be deficient in one or more minerals for good fertility, while a soil weathered from a mix of rock types (as in glacial, eolian or alluvial sediments) often makes more fertile soil. Parent material, in soil science, means the underlying bedrock from which soil horizons form. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ... Eolian (or aeolian) processes pertain to the activity of the winds. ... Alluvium is soil land deposited by a river or other running water. ... Fertile soil or Soil fertility is soil that can support abundant plant life, in particular the term is used to describe agricultural and garden soil. ...

Physical (mechanical) weathering

Mechanical weathering is the cause of the disintegration of rocks. The primary process in mechanical weathering is abrasion - the process by which clasts and other particles are reduced in size. However, chemical and physical weathering often go hand in hand. For example, cracks exploited by mechanical weathering will increase the surface area exposed to chemical action. Furthermore, the chemical action at minerals in cracks can aid the disintegration process. Glacially abraded rocks in western Norway near Jostedalsbreen glacier. ...

Thermal expansion

Thermal expansion, also known as onion-skin weathering, exfoliation, insolation weathering or thermal shock, often occurs in areas, like deserts, where there is a large diurnal temperature range. The temperatures soar high in the day, while dipping greatly at night. As the rock heats up and expands by day, and cools and contracts by night, stress is often exerted on the outer layers. The stress causes the peeling off of the outer layers of rocks in thin sheets. Though this is caused mainly by temperature changes, thermal expansion is enhanced by the presence of moisture. Geological exfoliation of granite at Enchanted Rock State Natural Area, Texas, USA Exfoliation in geology is a weathering process, mainly caused by freeze-thaw cycles. ... Thermal shock and thermal loading refer to the disfuntion (and perhaps, crack) of a material due to the heating, especially non-stationary and non-uniform. ... A dune in the Egyptian desert In geography, a desert is a landscape form or region that receives little precipitation. ... Stress is a measure of force per unit area within a body. ...

Freeze thaw weathering

A rock in southern Iceland fragmented by freeze-thaw action

This process can also be called frost shattering. This type of weathering is common in mountain areas where the temperature is around freezing point. Frost induced weathering, although often attributed to the expansion of freezing water captured in cracks, is generally independent of the water-to-ice expansion. It has long been known that moist soils expand or frost heave upon freezing as a result of water migrating along from unfrozen areas via thin films to collect at growing ice lenses. This same phenomena occurs within pore spaces of rocks. They grow larger as they attract liquid water from the surrounding pores. The ice crystal growth weakens the rocks which, in time, break up. Intermolecular forces acting between the mineral surfaces, ice, and water sustain these unfrozen films which transport moisture and generate pressure between mineral surfaces as the lens aggregates. Experiments show that chalk, sandstone and limestone do not fracture at the nominal freezing temperature of water of slightly below 0°C, even when cycled or held at low temperature for extended periods, as one would expect if weathering resulted from the expansion of water as froze. For the more porous types of rocks, the temperature range critical for rapid, ice-lens-induced fracture is -3 to -6°C, significantly below freezing temperatures.^[1][2] Image File history File linksMetadata Download high resolution version (4921x3247, 2806 KB) Beschreibung Licensing Summary File links The following pages link to this file: Weathering Metadata This file contains additional information, probably added from the digital camera or scanner used to create or digitize it. ... Image File history File linksMetadata Download high resolution version (4921x3247, 2806 KB) Beschreibung Licensing Summary File links The following pages link to this file: Weathering Metadata This file contains additional information, probably added from the digital camera or scanner used to create or digitize it. ... Frost heaving (or frost heave) occurs when soil expands upward or outward and contracts due to freezing and thawing. ... The Needles, situated on the Isle Of Wight, are part of the extensive Southern England Chalk Formation. ... Red sandstone interior of Lower Antelope Canyon, Arizona, worn smooth due to erosion by flash flooding over millions of years Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. ... For other uses, see Limestone (disambiguation). ...

Freeze induced weathering action occurs mainly in environments where there is a lot of moisture, and temperatures frequently fluctuate above and below freezing point—that is, mainly alpine and periglacial areas. An example of rocks susceptible to frost action is chalk, which has many pore spaces for the growth of ice crystals. This process can be seen in Dartmoor where it results in the formation of tors. For the climate of the mountains named the Alps, see climate) for a region above the tree-line. ... Periglacial refers to places in the edges of glacial areas, normally those related to past ice ages rather than those in the modern era. ... The Needles, situated on the Isle Of Wight, are part of the extensive Southern England Chalk Formation. ... High Willhays, the highest point on Dartmoor and southern England at 621 m (2037 ft) above sea level, with Yes Tor beyond. ... This article is about a geological formation. ...

Frost wedging

Formerly believed to be the dominant mode, ice wedging may still be a factor for weathering of nonporous rock, although recent research has demonstrated it less important than previously thought. Frost action, sometimes known as ice crystal growth, ice wedging, frost wedging or freeze-thaw occurs when water in cracks and joints of rocks freezes and expands. Water can exert pressures up to 21 megapascals (MPa) (2100 kgf/cm²) at −22 °C. This pressure is often higher than the resistance of most rocks and causes the rock to shatter.^[1][2] Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... The megapascal, symbol MPa is an SI unit of pressure. ... The unit kilogram-force (kgf, often just kg) or kilopond (kp) is defined as the force exerted by one kilogram of mass in standard Earth gravity. ... For other uses, see Celsius (disambiguation). ...

When water that has entered the joints freezes, the ice formed strains the walls of the joints and causes the joints to deepen and widen. This is because the volume of water expands by 9% when it freezes.

When the ice thaws, water can flow further into the rock. When the temperature drops below freezing point and the water freezes again, the ice enlarges the joints further.

Repeated freeze-thaw action weakens the rocks which, over time, break up along the joints into angular pieces. The angular rock fragments gather at the foot of the slope to form a talus slope (or scree slope). The splitting of rocks along the joints into blocks is called block disintegration. The blocks of rocks that are detached are of various shapes depending on rock structure. Talus (which is Latin for ankle-bone) may refer to: The talus bone, a bone connecting the leg to the foot Talos, a rock-throwing giant made of bronze in Greek mythology A sloping mass of loose rocks at the base of a cliff Scree, small broken rock found on... Scree or detritic cone is a term given to broken rock that appears at the bottom of crags, mountain cliffs or valley shoulders. ...

Pressure release

Pressure Release of granite.

In pressure release, also known as unloading, overlying materials (not necessarily rocks) are removed (by erosion, or other processes), which causes underlying rocks to expand and fracture parallel to the surface. Often the overlying material is heavy, and the underlying rocks experience high pressure under them, for example, a moving glacier. Pressure release may also cause exfoliation to occur. Image File history File linksMetadata Download high resolution version (2048x1360, 2712 KB) Summary Taken by Wing-Chi Poon on 2nd April 2005 in the Enchanted Rock State Natural Area of Texas, USA. The photo clearly shows the geological exfoliation of granite dome rock. ... Image File history File linksMetadata Download high resolution version (2048x1360, 2712 KB) Summary Taken by Wing-Chi Poon on 2nd April 2005 in the Enchanted Rock State Natural Area of Texas, USA. The photo clearly shows the geological exfoliation of granite dome rock. ... This article is about the geological formation. ... Exfoliation has several meanings: Dead skin cells? No: geological exfoliation of granite at Enchanted Rock State Natural Area, Texas, USA Exfoliation (cosmetology), is a cosmetic technique aimed at removing dead skin cells from the face and body. ...

Intrusive igneous rocks (e.g. granite) are formed deep beneath the earth's surface. They are under tremendous pressure because of the overlying rock material. When erosion removes the overlying rock material, these intrusive rocks are exposed and the pressure on them is released. The outer parts of the rocks then tend to expand. The expansion sets up stresses which cause fractures parallel to the rock surface to form. Over time, sheets of rock break away from the exposed rocks along the fractures. Pressure release is also known as "exfoliation" or "sheeting"; these processes result in batholiths and granite domes, an example of which is Dartmoor. For other uses, see granite (disambiguation). ...

Hydraulic action

This is when water (generally from powerful waves) rushes into cracks in the rockface rapidly. This traps a layer of air at the bottom of the crack, compressing it and weakening the rock. When the wave retreats, the trapped air is suddenly released with explosive force. The explosive release of highly pressurised air cracks away fragments at the rockface and widens the crack itself.

Salt-crystal growth (haloclasty)

The surface pattern on this pedestal rock is honeycomb weathering, caused by salt crystallisation. This example is at Yehliu, Taiwan.

Salt weathering of building stone on the island of Gozo, Malta

Salt weathering of sandstone near Qobustan, Azerbaijan.

Salt crystallization or otherwise known as Haloclasty causes disintegration of rocks when saline (see salinity) solutions seep into cracks and joints in the rocks and evaporate, leaving salt crystals behind. These salt crystals expand as they are heated up, exerting pressure on the confining rock. Image File history File links File links The following pages link to this file: Weathering Rock cycle ... Image File history File links File links The following pages link to this file: Weathering Rock cycle ... Image File history File linksMetadata Salt_weathering_in_gozo. ... Image File history File linksMetadata Salt_weathering_in_gozo. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (2048 × 1536 pixel, file size: 1. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (2048 × 1536 pixel, file size: 1. ... Red sandstone interior of Lower Antelope Canyon, Arizona, worn smooth due to erosion by flash flooding over millions of years Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. ... Qobustan is an administrative district, or rayon, of Azerbaijan. ... The surface pattern on this pedestal rock is honeycomb weathering, caused by salt crystallisation. ... Annual mean sea surface salinity for the World Ocean. ... Crystal (disambiguation) Insulin crystals A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ...

Salt crystallization may also take place when solutions decompose rocks (for example, limestone and chalk) to form salt solutions of sodium sulfate or sodium carbonate, of which the moisture evaporates to form their respective salt crystals. For other uses, see Limestone (disambiguation). ... The Needles, situated on the Isle Of Wight, are part of the extensive Southern England Chalk Formation. ... The sulfate anion, SO42− The structure and bonding of the sulfate ion In inorganic chemistry, a sulfate (IUPAC-recommended spelling; also sulphate in British English) is a salt of sulfuric acid. ... Sodium carbonate (also known as washing soda or soda ash), Na2CO3, is a sodium salt of carbonic acid. ...

The salts which have proved most effective in disintegrating rocks are sodium sulfate, magnesium sulfate, and calcium chloride. Some of these salts can expand up to three times or even more. Magnesium sulfate (or sulphate) is a chemical compound containing magnesium and sulfate, with the formula MgSO4. ... R-phrases S-phrases , , Related Compounds Other anions calcium fluoride calcium bromide calcium iodide Other cations magnesium chloride strontium chloride Supplementary data page Structure and properties n, εr, etc. ...

It is normally associated with arid climates where strong heating causes strong evaporation and therefore salt crystallisation. It is also common along coasts. An example of salt weathering can be seen in the honeycombed stones in sea walls. In general terms, the climate of a locale or region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life. ... A seawall is a form of hard coastal defense that are constructed on the inland part of a coast to reduce the effects of strong waves, typically to defend the coast around a town or harbour from erosion. ...

Biotic weathering

Living organisms may contribute to mechanical weathering (as well as chemical weathering, see 'biological' weathering below). Lichens and mosses grow on essentially bare rock surfaces and create a more humid chemical microenvironment. The attachment of these organisms to the rock surface enhances physical as well as chemical breakdown of the surface microlayer of the rock. On a larger scale seedlings sprouting in a crevice and plant roots exert physical pressure as well as providing a pathway for water and chemical inlfitration. Burrowing animals and insects disturb the soil layer adjacent to the bedrock surface thus further increasing water and acid infiltration and exposure to oxidation processes. For other things named Lichen, see: Lichen (disambiguation). ... For other uses, see Moss (disambiguation). ...

Chemical weathering

Chemical weathering involves the change in the composition of rocks, often leading to a 'break down' in its form. This type of weathering happens over a period of time.

Dissolution

Rainfall is naturally slightly acidic because atmospheric carbon dioxide dissolves in the rainwater producing weak carbonic acid. In unpolluted environments, the rainfall pH is around 5.6. Acid rain occurs when gases such as sulphur dioxide and nitrogen oxides are present in the atmosphere. These oxides react in the rain water to produce stronger acids and can lower the pH to 4.5 or even 3.0. Sulfur dioxide, SO₂, comes from volcanic eruptions or from fossil fuels, can become sulfuric acid within rainwater, which can cause solution weathering to the rocks on which it falls. For other uses, see Acid (disambiguation). ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... For other uses, see PH (disambiguation). ... The term acid rain is commonly used to mean the deposition of acidic components in rain, snow, fog, dew, or dry particles. ... Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. ... R-phrases S-phrases , , , Flash point Non-flammable Related Compounds Related strong acids Selenic acid Hydrochloric acid Nitric acid Related compounds Hydrogen sulfide Sulfurous acid Peroxymonosulfuric acid Sulfur trioxide Oleum Supplementary data page Structure and properties n, εr, etc. ...

One of the most well-known solution weathering processes is carbonation, the process in which atmospheric carbon dioxide leads to solution weathering. Carbonation occurs on rocks which contain calcium carbonate such as limestone and chalk. This takes place when rain combines with carbon dioxide or an organic acid to form a weak carbonic acid which reacts with calcium carbonate (the limestone) and forms calcium bicarbonate. This process speeds up with a decrease in temperature and therefore is a large feature of glacial weathering. For the chemical reaction forming calcium carbonate, see carbonatation. ... Calcium carbonate is a chemical compound, with the chemical formula CaCO3. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... An organic acid is an organic compound that is an acid. ... A weak acid is an acid that does not fully ionize in solution; that is, if the acid was represented by the general formula HA, then in aqueous solution a significant amount of undissolved HA still remains. ... Carbonic acid (ancient name acid of air or aerial acid) has the formula H2CO3. ... Calcium bicarbonate (Ca(HCO3)2), also called calcium hydrogencarbonate, is a compound which exists only in solution. ...

The reactions as follows:

CO₂ + H₂O -> H₂CO₃

carbon dioxide + water -> carbonic acid

H₂CO₃ + CaCO₃ -> Ca(HCO₃)₂

carbonic acid + calcium carbonate -> calcium bicarbonate

Carbonation on the surface of well-jointed limestone produces a dissected limestone pavement which is most effective along the joints, widening and deepening them.

Hydration

Hydration is a form of chemical weathering that involves the rigid attachment of H+ and OH- ions to the atoms and molecules of a mineral.

When rock minerals take up water, the increased volume creates physical stresses within the rock. For example iron oxides are converted to iron hydroxides and the hydration of anhydrite forms gypsum.

A freshly broken rock shows differential chemical weathering (probably mostly oxidation) progressing inward. This piece of sandstone was found in glacial drift near Angelica, New York

Image File history File links Download high resolution version (1600x1067, 832 KB)A freshly broken rock shows differential chemical weathering progressing inward. ... Image File history File links Download high resolution version (1600x1067, 832 KB)A freshly broken rock shows differential chemical weathering progressing inward. ... Red sandstone interior of Lower Antelope Canyon, Arizona, worn smooth due to erosion by flash flooding over millions of years Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. ... This article is about geological phenomena. ... Angelica, New York is a village and a town in Allegany County, New York. ...

Hydrolysis

Hydrolysis is a chemical weathering process affecting Silicate minerals. In such reactions, pure water ionizes slightly and reacts with silicate minerals. An example reaction: Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by reaction with water. ...

Mg₂SiO₄ + 4H⁺ + 4OH^- ⇌ 2Mg²⁺ + 4OH^- + H₄SiO₄

olivine (forsterite) + four ionized water molecules ⇌ ions in solution + silicic acid in solution

This reaction results in complete dissolution of the original mineral, assuming enough water is available to drive the reaction. However, the above reaction is to a degree deceptive because pure water rarely acts as a H⁺ donor. Carbon dioxide, though, dissolves readily in water forming a weak acid and H⁺ donor. The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ... Forsterite (Mg2SiO4) is the magnesium rich end-member of the olivine solid-solution series. ...

Mg₂SiO₄ + 4CO₂ + 4H₂O ⇌ 2Mg²⁺ + 4HCO₃^- + 4H₄SiO₄

olivine (forsterite) + carbon dioxide + water ⇌ Magnesium and bicarbonate ions in solution + silicic acid in solution

This hydrolysis reaction is much more common. Carbonic acid is consumed by silicate weathering, resulting in more alkaline solutions because of the bicarbonate. This is an important reaction in controlling the amount of CO₂ in the atmosphere and can affect climate. The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ... Forsterite (Mg2SiO4) is the magnesium rich end-member of the olivine solid-solution series. ... Carbonic acid (ancient name acid of air or aerial acid) has the formula H2CO3. ... In chemistry, a silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. ... The common (Arrhenius) definition of a base is a chemical compound that either donates hydroxide ions or absorbs hydrogen ions when dissolved in water. ... For baking soda, see Sodium bicarbonate In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. ...

Aluminosilicates when subjected to the hydrolysis reaction produce a secondary mineral rather than simply releasing cations. Aluminosilicate minerals are minerals that have the basic structure and composition of AlSiO4. ...

2KAlSi₃O₈ + 2H₂CO₃ + 9H₂O ⇌ Al₂Si₂O₅(OH)₄ + 4H₄SiO₄ + 2K⁺ + 2HCO₃^-

Orthoclase (aluminosilicate feldspar) + carbonic acid + water ⇌ Kaolinite (a clay mineral) + silicic acid in solution + potassium and bicarbonate ions in solution

Orthoclase (KAlSi3O8) is an important tectosilicate mineral, which forms igneous rock. ... Kaolin redirects here. ...

Oxidation

Within the weathering environment chemical oxidation of a variety of metals occurs. The most commonly observed is the oxidation of Fe²⁺ (iron) and combination with oxygen and water to form Fe³⁺ hydroxides and oxides such as goethite, limonite, and hematite. This gives the affected rocks a reddish-brown coloration on the surface which crumbles easily and weakens the rock. This process is better known as 'rusting'. The most fundamental reactions in chemistry are the redox processes. ... For other uses, see Iron (disambiguation). ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colourless (gas) colourless (liquid) Standard atomic weight 15. ... Goethite, named after the German polymath Johann Wolfgang von Goethe, is an iron bearing oxide mineral found in soil and other low temperature environments. ... Limonite Limonite Limonite is a ferric hydrate of varying composition, the generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as Limonite often contains a varying amount of oxide compared to hydroxide. ... Hematite, also spelled haematite, is the mineral form of Iron(III) oxide, (Fe2O3), one of several iron oxides. ... This article is about the type of corrosion. ...

Biological

A number of plants and animals may create chemical weathering through release of acidic compounds.

The most common form of biological weathering is the release of chelating compounds, i.e acids, by plants so as to break down aluminium and iron containing compounds in the soils beneath them.^{[citation needed]} Extreme release of chelating compounds can easily affect surrounding rocks and soils, and may lead to podsolisation of soils. Chelation (from Greek χηλή, chelè, meaning claw) is the process of reversible binding of a ligand, the chelator or chelating agent, to a metal ion, forming a metal complex, the chelate. ... Aluminum redirects here. ... For other uses, see Iron (disambiguation). ... Podsol (also spelled Podzol, or known as Spodosol) is the typical soil of coniferous, or Boreal forests. ...

Carbonation

Carbon dioxide is added to rock minerals in the form of carbonic acid, which has derived its CO₂ content from the atmosphere and vegetation. Carbonic acid is much more effective than pure water in attacking feldspar and other minerals. Silica and potassium-sodium carbonates are thus dissolved.

Building weathering

Buildings made of any stone, brick or concrete are susceptible to the same weathering agents as any exposed rock surface. Also statues, monuments and ornamental stonework can be badly damaged by natural weathering processes. This is accelerated in areas severely affected by acid rain. The term acid rain is commonly used to mean the deposition of acidic components in rain, snow, fog, dew, or dry particles. ...

See also

• Biorhexistasy
• Eluvium
• Erosion
• Pedogenesis
• Soil production function
• Space weathering
• Spheroidal weathering

The Theory of Biorhexistasy describes climatic conditions necessary for periods of soil formation (pedogenesis) separated by periods of soil erosion. ... In geology, Eluvium or eluvial deposits are those geological deposits and soils that are derived by in situ weathering or weathering plus gravitational movement or accumulation. ... For morphological image processing operations, see Erosion (morphology). ... Pedogenesis or soil evolution (formation) is the process by which soil is created. ... Soil production function refers to the rate of bedrock weathering into soil as a function of soil thickness. ... Please wikify (format) this article as suggested in the Guide to layout and the Manual of Style. ... Spheroidal weathering is a type of physical and chemical weathering that creates rounded boulders and helps to create domed monoliths. ...

References

1. ^ ^{a b} J. B. Murton, R. Peterson, J.-C. Ozouf, Science 314, 1127 (2006).
2. ^ ^{a b} J. G. Dash, A. W. Rempel, J. S. Wettlaufer, Rev. Mod. Phys. 78, 695 (2006).